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1st EICAC MeetingQuestions/Comments
on ELIC Design JLab ELIC Machine Design Team
Nov. 3, 2009
ELIC Design Issues
• Ultra short bunch ion beam – Formation of high intensity beam: electron cooling and intra-
beam scattering (Slava Derbenev, Yuhong Zhang)
– Beam instability and life time (Byung Yunn)
– Beamstrahlung (Slava Derbenev)
– CSR effect (Rui Li)
• ELIC ring and interaction region (IR) design– Choice of figure-8 ring design (Slava Derbenev)
– Asymmetric final focusing at interaction region (Alex Bogacz)
– Lattice design with sufficient dynamical aperture (Alex Bogacz and Yves Roblin)
Forming of High Intensity High Bunch Repetition Ion Beams w/ Electron Cooling
Length
(m)
Max.
Energy
(GeV/c)
Cooling
SchemeProcess
SRF linac 0.2 Full stripping
Accumulator
-Cooler Ring
(Pre-booster)
~100 3DC
electron
Stacking/
accumulating
Energy boosting
Low energy
ring
(booster)
~630 12Electron
(ERL)
Fill ring
Energy boosting
Medium
energy
collider ring
~630 60Electron
(ERL)
Energy boosting
SRF bunching
Ion
source
SRF
Linac
pre-booster-
Accumulator
ring
Booster-
low energy
collider ring
Medium
energy ion
collider ring
To high
energy ion
collider ring
cooling
Initial
Cooling
after
bunching
& boost
Steady
state
Mode
Momentum GeV/MeV 12 / 6.55 60 / 32.7 60 / 32.7
Beam current A 0.6 / 3
Particles/Bunch 1010 0.74 / 3.75
Bunch length mm 200/200 10 / 30 5 / 15
Momentum spread 10-4 5 / 1 5 / 1 3 / 1
Horizontal
emittance, norm.
µm 4 1 0.56
Vert. emitt., norm. µm 4 1 0.11
Laslett’s tune shift proton 0.002 0.006 0.1
Cooling length
/circumference
m/m 15 / 640
Cooling time s 92 162 0.2
IBS growth time
(longitudinal)
s 0.9
• Ultra short (5 mm) ion bunch achieved with very
small bunch charge, ~ 7x109/bunch
• Staged electron cooling (at injection, final and
steady state) is essential.
• We have a working concept, next level design
work is underway.
Ion Beam Stability• Single bunch instability (1010/bunch)
Safe from longitudinal microwave instability and
transverse mode coupling instability
• longitudinal impedance less than 9 Ω
• transverse impedance less than 200 MΩ/m
• Multi-bunch instabilityActive feedbacks necessary to control longitudinal and
transverse coupled bunch instabilities
• Intra-beam scatteringBeam cooling necessary to counteract growths
• Beam life timeTouschek life time ~17 hrs
Beamstrahlung of Electron
Proton beam parameters at 60 GeV
• Energy loss relative to radiation in arcs : 0.05% per IP
• Energy diffusion due to quantum beamstrahlung: 0.5% per IP
• Impact on emittance (due to dispersion-prime):
may require zero dispersion before the final focus quads
– Needs further work
CSR Estimation for the MEIC Ion Ring
• Parameters
m 0.02b aperture assume
m 30 mm, 5 ,1074.0 GeV, 60 10
RNE zpp
• CSR is shielded for the ion ring
mm 3.0 thCSR is shielded when
• No microbunching instability can be developed
No coherent radiation at mm 5 z
Landau damping allows instability to develop only
for , which is bigger than bunch lengthm 9.0
Choice of Figure-8 Ion Rings
• Figure-8 optimum for polarized ion beams– Simple solution to preserve full ion polarization by avoiding
spin resonances during acceleration
– Energy independence of spin tune
– g-2 is small for deuterons; Figure-8 ring is the only practicalway to arrange longitudinal spin polarization at interaction point.
– Allows multiple interactions in a same straight – can help with chromatic correction
• Only disadvantage is small cost increase– There are no technical disadvantages
Figure-8 Collider Ring – Optics
657.6850
Thu Oct 29 19:35:55 2009 OptiM - MAIN: - C:\Working\E LIC\MEIC\Optics\E lectron Ring\Ring_full_period.opt
800
00
6-6
BE
TA
_X
&Y
[m]
DIS
P_
X&
Y[m
]
BE TA_X BE TA_Y DIS P_X DIS P_Y
Arc inward Arc outwardStraight + 2 IR Straight disp.
-5000
-3000
-1000
1000
3000
5000
-15000 -10000 -5000 0 5000 10000 15000
x [cm]
z [cm]
Figure-8 Collider Ring - Footprint
600
total ring circumference: 660 m
L = 150 m
C = 180 m
Figure-8 Collider Ring – Arc Optics
1790
Thu Oct 29 20:02:11 2009 OptiM - MAIN: - C:\Working\ELIC\ME IC\Optics\Electron Ring\Arc_in.opt
15
0
0.3
-0
.3
BE
TA
_X
&Y
[m
]
DIS
P_
X&
Y[m
]
BE TA_X BE TA_Y DIS P_X DIS P_Y
phase adv./cell (Dx,y= 1200)
36 FODO cells, B, total arc length: 179 m
Minimized emittance dilution due to quantum excitations
Quasi isochronous arc to alleviate bunch lengthening (a~10-5)
Dispersion pattern optimized for chromaticity compensation with sextupoles
Dipoles
$Lb=150 cm
$B=11.6 kG.
Quadrupoles
$Lq=50 cm
$G= ±4.5 kG/cm
11 GeV
27.14270
Thu Oct 29 08:54:57 2009 OptiM - MAIN: - N:\bogacz\E LIC\MEIC\Optics\E lectron Ring\e_6m_LR_6_period.opt
0.5
0
0.5
0
Siz
e_
X[c
m]
Siz
e_
Y[c
m]
Ax_bet Ay_bet Ax_disp Ay_disp27.14270
Thu O ct 29 08:54:10 2009 O ptiM - MAIN: - N:\bogacz\E LIC\MEIC\O ptics\E lectron Ring\e_6m_LR_6_period.opt
800
00
50
BE
TA
_X
&Y
[m
]
DIS
P_
X&
Y[m
]
BE TA_X BE TA_Y DIS P_X DIS P_Y
Interaction Region Optics
6
6
85 10
17 10
x
N
y
N
m
m
*
*
25
5
x
y
mm
mm
l * = 6m
IP
FF triplet : Q3 Q2 Q1 Q1 G[kG/cm] = -3.4
Q2 G[kG/cm] = 2.1
Q3 G[kG/cm] = -4.1
vertical focusing first
l * = 6m
IP
Natural Chromaticity: x=-305 y =-425
Collider Ring – a pair of IRs Optics
350158
Thu Oct 29 08:58:43 2009 OptiM - MAIN: - N:\bogacz\ELIC\ME IC\Optics\Electron Ring\Ring_full_period.opt
800
00
6-6
BE
TA
_X
&Y
[m]
DIS
P_
X&
Y[m
]
BE TA_X BE TA_Y DIS P_X DIS P_Y
328.8420
Thu Oct 29 19:47:28 2009 OptiM - MAIN: - C:\Working\ELIC\ME IC\Optics\Electron Ring\Arc_in_Straight_IR.opt
800
00
6-6
BE
TA
_X
&Y
[m
]
DIS
P_
X&
Y[m
]
BE TA_X BE TA_Y DIS P_X DIS P_Y
IR Chromaticity CompensationUncompensated dispersion pattern coming out of the Arc
10 14
sext
sext
sext
g
1 1, , 0 , 14 4
IR i i i i
x y x y x y
i i
g ds k
1
1
1[ ]
y yB Bek dl dl m
B x pc x
Natural Chromaticity: x = -650 y = -990
350158
Thu Oct 29 08:58:43 2009 OptiM - MAIN: - N:\bogacz\ELIC\ME IC\Optics\Electron Ring\Ring_full_per iod.opt
800
00
6-6
BE
TA
_X
&Y
[m]
DIS
P_
X&
Y[m
]
BE TA_X BE TA_Y DIS P_X DIS P_Y
Compensating sextupole strength: g 1= 0.15
m-2
Issues and Status
Question Assessment Status
Ultra short ion bunch • Forming ultra-short ion bunch
• Beam dynamics and instability
Have a workable concept
Checked cooling & IBS rates
Ion beam lifetime General question
(also beam instabilities)
Checked leading causes
(Byung Yunn)
Figure-8 ion ring choice Closed
Luminosity lifetime
reduction due to
beamstrahlung at IP
Checked (Slava Derbenev)
5 mm β* in x and y Good observation β* in x changed to 25 mm
Electron linear optics complete
Ion ring will be similar
Lattice design with
sufficient dynamical
aperture
Needs linear lattices, chromatic
correction, and tracking studies
In progress. Tracking studies
will start (Alex Bogacz, Yves
Roblin)
CSR effect for unusually
short ion bunch
Effects are small.
Closed (Rui Li)
Backup Slides
Accelerator Design Related Comments• “Of the two alternatives presented, the JLAB concept is in essence a new facility even though built
around the existent CEBAF. As such, a lot of (basic) accelerator design work has to be done. The ion ring has a number of challenging beam parameters (e.g. the ultra-short ion bunches, beam lifetimes, figure-8 rings etc.). This is not to ignore the challenges for eRHIC. The common R&D effort should focus on the technologies needed for both approaches: cooling, MDI, beam-beam investigations, the various crabbing schemes. Beyond this, an R&D plan involving both labs for the eventual unified proposal will need to be developed. It would be good to see a detailed common plan addressing these issues at the next meeting, with deliverables and resources needed to get to a buildable design for the NSAC Long Range Plan in 2012. ”
• ”It would appear that it would be better to have a detailed review of the designs of the accelerator(s) by more accelerator experts if possible. A few specific comments are listed in the following; in my opinion, any one of them may have a possibility to be a show stopper and thus needs to be carefully considered.For eRHIC: For the ring-ring scheme, the Hirata-Keil effect should be looked at carefully as the density of the resonance lines increases three-fold. The very high disruption assumed for the ring-ERL scheme needs verification, as the electron bunch becomes unstable during a single collision which should affect the proton or ion beam to cause dilution of the emittance.For ELIC: The luminosity lifetime will be much shorter than 24 hours due to the beam loss from Bremsstrahlung at the interaction point (IP). If so, much more frequent injection of electrons will be needed but such injections may heat up the protons or ions. The very tight focusing at the IP, 5 mm beta* in x and y, does not look feasible with the proposed length (7 m) between the IP and the first quadrupole, due to associated chromaticity and nonlinear effects to reduce the dynamic aperture. A consistent lattice should be shown with sufficient dynamic aperture. As the bunch length of the proton beam is unusually short, effects unfamiliar to a proton beam such as coherent synchrotron radiation may happen.”
ERL Based Circulator Electron Cooler
ion bunch
electron
bunchElectron
circulator
ring
Cooling section
solenoid
Fast beam
kicker
Fast beam
kicker
SRF
Linac
dumpelectron
injector
energy
recovery
path
Circulator ring by-pass
Path length
adjustment
(synchronization)
ELIC e-Cooler Design ParametersMax/min energy of e-beam MeV 33/8
Electrons/bunch 1010 3.75
bunch revolutions in CCR ~300
Current in CCR/ERL A 3/0.01
Bunch repetition in CCR/ERL MHz 500/1.67
CCR circumference m 80
Cooling section length m 15
Circulation duration s 27
Bunch length cm 1-3
Energy spread 10-4 1-3
Solenoid field in cooling section T 2
Beam radius in solenoid mm ~1
Beta-function m 0.5
Thermal cyclotron radius m 2
Beam radius at cathode mm 3
Solenoid field at cathode KG 2
Laslett’s tune shift @60 MeV 0.07
Longitudinal inter/intra beam
heating
s 200
• Number of turns in circulator cooler
ring is determined by degradation of
electron beam quality caused by
inter/intra beam heating up and space
charge effect.
• Space charge effect could be a leading
issue when electron beam energy is
low.
• It is estimated that beam quality (as
well as cooling efficiency) is still good
enough after 100 to 300 turns in
circulator ring.
• This leads directly to a 100 to 300
times saving of electron currents from
the source/injector and ERL.
Ion Beam Instability
0.06s 43 10 5l mm
0.75bI mA 1010pN
3100threshold l
b
L
eff
hVI
Z C
n
9L
eff
Z
n
Note: Ion ring parameters are E = 60GeV, C = 630m, h = 3150, η = 0.01, V = 43 MV,
Potentially dangerous instabilities for ion ring are longitudinal microwave instability,
transverse mode coupling instability, longitudinal and transverse coupled bunch instabilities.
Design current ( ) leads to following limits on impedances
Longitudinal Microwave Instability:
momentum aperture = 0.38 %
RZ
be
E
IaveffT
s
b
4
190avT eff
Z Gb
16
Im( )
sthreshold lb
T eff av
E
eI
Z C
Im( ) 1.9T eff avZ G
Transverse Microwave Instability:
Transverse Mode Coupling Instability:
Ion Beam Instability (cont.)
52 348
Im( )
threshold lb
eff
h VI
Z C
n
Im( ) 30eff
Zm
n
Rcm
Nex
xzp
cp
s
22/33332
4
1
8
log 1.8s s
222/53332
4
1 12
16
log
xxxzp
cp
x
R
cm
Ne1.7x s
2
1
5 3 2
'
0.5618ln 1.5
p p
Touschek
x A B A
r cN
V
'
1A
x aperture
p
p
D
17Touschek hrs
Longitudinal Coupled Bunch Instability:
Intrabeam Scattering Growth Rates (logc = 10 is assumed):
Touschek Lifetime:
,
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